The instant invention is related to an atmospheric pressure discharge system for generating a plasma discharge for exciting samples to be analyzed by optical emission spectrometry.
Previously, such plasma discharge systems have included microwave-induced plasma and inductively coupled plasma. However, these systems have drawbacks, set forth below, which the instant invention overcomes.
In detecting elements in air, water or solid samples, for example, for use in environmental research or other types of research, such microwave-induced plasma (MIP) systems have been well known for producing a plasma discharge to excite samples to be analyzed by known optical emission spectrometry systems. Such MIP systems have also been known as single electrode plasma torch systems. In using an MIP system, elements may be detected, however, such systems require a magnetron tube operating at a frequency of 2,450 MHz for example.
The MIP system can use helium as a carrier gas and thus can detect non-metals. However, the employment of the magnetron tube also requires a high voltage of from 1000 V to 2000 V to operate the magnatron tube. Additionally, it should be noted that the MIP system requires a high flow rate for the gas flowing through it. A flow rate of 3 to 4 liters/min. is required to properly cool the electrodes. A sufficient exhaust velocity of gas from the plasma chamber is necessary in order to prevent leakage of surrounding air into the plasma chamber, thus causing inaccuracies in the detection of the emission spectra.
Another system for generating a plasma discharge is the inductively coupled plasma (ICP). The ICP system uses only Argon for a carrier gas and thus cannot be used for detecting non-metals, because a helium discharge is essential for detecting non-metals. The ICP system has a relatively large gas consumption and requires extremely large equipment for operation.
The above systems, single electrode plasma torch (MIP) and ICP, of providing a plasma discharge for optical emission spectrometry require large amounts of equipment for performing the necessary analysis. Such large equipment demands makes the use of the above systems incompatible with taking field measurements in environmental research or the like.